Another Ah/battery question

[claws]

I'll be picking up my new 2021 Hawk Shell in December and am trying to get my electricity usage figured out. The shell is bare bones with only a heater, cook top, Fantastic Fan, and LED lights. It will have the standard 75 Ah AGM battery and I will be adding a portable 100W solar panel that can be aimed at the sun during daylight hours. Given the 50% draw down limit of the battery I will have 37.5 Ah available. I'm getting a Dometic cfx26 DC fridge. Here are my simple minded calculations for power usage. The only constant drain on the battery will be the fridge at .8 Ah. With no sun light for 12 hours a day that equates to 9.6 Ah drain between solar panel charges. I will run the heater fan no more than an hour a day, and the Fantastic Fan no more than 2 hours a day. i don't know what the heater fan and roof vent fan use but it seems that since I have about 27.5 Ah left after deducting the fridge power needs over night I should have plenty of power for my needs. I'm also figuring that my solar panel at only 50W real output would generate 33.3Ah in the course of 8 hours. This seems to be too good to be true. What am I forgetting, or getting wrong with these calculations?
Thanks,
Kim

 

[rando]

Based on experience, I think you will be mostly OK with a 75Ah battery powering a fridge, furnace, fans and lights, as long as your are in the sunnier parts of the country. You may be in trouble if you find yourself in extended overcast or in the shade as you don't have much margin built in. More and roof mounted solar is probably your best bet.

A couple of things to consider:

The 50% 'rule' is not really a rule and in a weight and space limited application like a FWC you would be better served to run your batteries down to 80% and accept that you will need to replace them more often.

Your solar estimates are optimistic, particularly for a portable panel - will you really be putting and leaving it out for 8 hours a day, every day? You may be better served with a larger roof mounted panel that just runs without needing to be deployed. With a roof mounted panel, a reasonable conservative estimate for a sunnier region is the equivalent of 5 hrs a day at the full rated current. With a similar setup, my 160W panel worked fine with the 75Ah battery, 90% of the time.

Will the camper be connected to the truck alternator, and get charge from that? If you drive most days, this can add to your budget.

You also need to consider that the fridge will run (more) when the sun is up. The fridge will be consuming ~20Ah per day and this all counts in your budget.

 

[claws]

Thanks for the reply, Rando. I hadn't considered running the battery down by 80% but since I want to eventually replace the AGM with a Lipo, this sounds like a good idea. I'm considering the 100W portable panel (a flexible panel from Renogy) for weight savings and the ability to deploy it in the sun if my camper is in the shade. I probably won't be driving every day but could run the engine/alternator for a half hour a day if needed. I would like a roof mounted solar panel but I'm really trying to keep the weight down since the payload rating of my 2014 F150 is so low. Also, raising and lowering the roof is already problematic given my age related arthritis and the added weight of a panel on top would only aggravate the problem.

Kim

 

[rando]

You could consider a 175W semi-flexibe panel for the roof, these are very light, but as a result may not have longevity or reliability of a rigid panel. You could consider either the crank up speaker stand or a linear actuator to help in raising the roof. I am too young to be complaining, but 90% of the time I use my linear actuator to put the roof up.

Only you know your style of camping, but my experience is that the portable panels really don't get used very much as they need to be moved/aimed, and often you don't want to leave them out when unattended due to wind or possibly theft.

Unfortunately, idling the truck for half an hour won't do much unless you add large wires back to the camper, and/or a DC-DC charger (and even then you won't get more than 15Ah or so).

 

[Utah]

I have a very similar setup (Hawk shell). I am running a National Luma fridge, the furnace, LED lights and a vent fan off the batteries. Plus also charging phones, etc in the camper occasionally. I have two 84 AH rated batteries (so total 168 AH) in the Hawk. The batteries were installed in Jan 2016 (so over 5 years old now. I have not added solar panels yet because I really haven’t needed to. I typically drive to a campsite and stay 1 or 2 nights and then charge from the truck alternator while driving. Normally I am driving somewhere every day, but not always.

My real world experience over the past year (which I can now track since I installed a Victron battery monitor) ranges 15 to 25 AHr draw per day (24 hr period). The biggest variable seems to be how much I am running the furnace at night.

With my setup and my use, the deepest draw down on the batteries over 8 trips in the past year has been 34 AHr. So, my batteries are getting recharged normally from the truck without depleting much of the capacity.

Hope this helps.

 

[ri-f]

Kim, I think if you are extremely frugal in your total energy usage, you could run your fridge fulltime and squeak by on a 75 ah AGM. But you're not giving yourself much leeway, and that's assuming that you are camping in a perfect, sunny world.

You could swap out your 75 ah AGM for a 100 ah LiFePo4 and put an efficient, durable 6 lb. 160 w Overland Solar panel on your roof and supplement that with a portable panel on the ground if you felt you wanted some extra amps coming in. Although I think you could get away without the portable panel. That would give you a comfortable amount of energy to handle your fridge and LEDs and fan and charge up some phones or tablets or a camera, etc. It would likely allow you to stay in one place for a few days without needing to leave because you need to charge up by driving.

Of course you could stick with what you've got and use a Yeti cooler, too, which will require ice blocks every 4 to 6 days or so, but it will save you 20 amp hours.a day, which is the bulk of your electrical consumption.

Your location and climate where you camp will be the primary factors that will determine your energy requirements. So, do you live in a perfect world? Or do you need to compensate with some additional energy coming in and some additional battery capacity? Yeti coolers work well if you don't mind swapping out ice blocks.

Rich

 

[claws]

Thanks Rando, Bird Skier, and ri-f. I think I could get by with my proposed set up for two days and nights without running the truck. If I had to run the furnace all night that would change things, but I usually just ran it for a few minutes at night and in the morning in my 16' travel trailer. If I find that I want to stay in one place for more than a couple of days then I'll consider a Lipo upgrade and a roof mounted solar panel. For now I want to keep things as simple and light as possible. The Yeti cooler won't work for me, ri-f. I'm too old and lazy to hump ice blocks.
Thanks for all the suggestions and info. I've learned a lot.

Kim

 

[ri-f]

Kim, good luck with the new shell. For just 1-2 days, I agree, you should be just fine with what you you are suggesting, as long as you leave with a fully charged battery. You can always upgrade later if you need more power and storage..

Rich

 

[larryqp]

Just two more things to consider.
1- When you get your new camper, your battery will be new and therefore that is the best time to add a second battery of equal size and type. So for $100-150 or so you double your capacity and camp worry free.
2- Your new battery will also be worth the most if you wanted to sell it, so upgrading to Li immediately would allow you to sell the battery and invest that money towards a Li battery.


Just more info to scramble your brain, but you have many months to mull it over.

Welcome to the forum and the FWC family

 

[claws]

Thanks for the info, Larry. Since weight is a big concern for me another AGM battery just won't work. Neither will the two 6 volt battery option. Hopefully Lipo batteries will be a little cheaper by December when I pick up my camper. I'm not sure what's involved in switching to Lipo. Hopefully it's nothing more than a battery swap.

Kim

 

[ramblinChet]

I tend to view the truck-FWC-energy as a system. If our truck and camper combinations fall into the $50-100k range then why would be hesitate at spending $1-3k for a healthy energy system with sufficient capacity?

For the past three years I have been using a single 100 Ah LiFePO4 in my Jeep to power my National Luna 80 L fridge but I am planning to install another and leave room for a possible third in my Grandby. My solar system will have a minimum of 500-600 watts although if I can squeeze 1 kW up there I certainly will. My goal is to use electric as a primary source for refrigeration, cooking, etc.

Personally, I do not wish to drive around in a $75k overland rig worrying about power supply issues the majority of the time. My goal is to build a rig that permits me to focus on the natural beauty I am in and not to worry about my support system.

 

[claws]

I can't argue with that logic, Chet. I probably will never be out and about long enough at one time to require energy needs like yours, but will probably upgrade to a lipo battery at some point. Right now weight is a big issue for me due to the limited payload capacity of my truck. Thanks for your comments.

Kim

 

[Wallowa]

I can't argue with that logic, Chet. I probably will never be out and about long enough at one time to require energy needs like yours, but will probably upgrade to a lipo battery at some point. Right now weight is a big issue for me due to the limited payload capacity of my truck. Thanks for your comments.

Kim

Li batteries are significantly lighter than AGMs....since you mentioned weight as a 'big issue'

 

[ramblinChet]

Good point Kim and I must constantly remind myself that each of us are building vehicle and camper combination for very different reasons with vastly different goals in mind. My build is geared towards full time for 3-5 or maybe more years in a wide variety of climates with a large dose of remoteness added to the mix.

The great thing is we have many folks here with every imaginable build configuration and we get to ask questions and see pictures!

 

[BBZ]

I run a small fridge/freezer during the day hours when the batteries are most charged and make my own ice blocks from old juice containers. I then unplug at night and throw in the cooler. This works great and makes it so I don't have to use energy at night.

 

[Wallowa]

I run a small fridge/freezer during the day hours when the batteries are most charged and make my own ice blocks from old juice containers. I then unplug at night and throw in the cooler. This works great and makes it so I don't have to use energy at night.

Good ploy when needed...another idea is to park so that your fridge is on the shaded side of the camper...no solar heating.